One of the main goals of this study will be to make accurate evaluations of the amount of accommodation developed by different human and animal subjects in comparable situations and to relate this amount to such variables as fixation distance, convergence, pupil size, lens thickness, optical components, retinal image size, spasm of accommodation, astigmatism intraocular pressure and retinal blur using a variety of optometers, ultrasound, phakometry and other measuring techniques and to relate these findings to refractive error. A second main goal will be to continue the present longitudinal studies of the optical components of refraction to determine the effects of heredity and environmental factors on the development of myopia in animals and humans, particularly the Eskimos at Barrow, Alaska. To date these studies suggest that a spasm of accommodation appears to be related to the development of myopia and that there is a certain amount of growth of the eye that is unrelated to environment but that after cessation of this growth any further growth appears to be related to visual demand. The longitudinal studies should make such relations clear and assist in developing techniques of predicting and controlling the development of myopia. A third main goal will be to determine how accommodation could be related to the development of myopia. These studies will be carried out primarily on monkeys and will involve the use of iridectomized animals, drug stimulation, near visual situations, intraocular pressure measurements, blood flow relationships, outflow facility and a variety of other measurements to determine what happens during the process of accommodation that could result in the development of myopia.